The invention discloses a main shaft sealing overhauling method. The main shaft sealing overhauling method comprises the following steps: S1, removing a water tank and an upper cover from top to bottom in sequence, lifting a floating ring by a certain height; S2, checking whether axial jumpiness of an anti-wearing plate can meet a design requirement or not by adopting a jigger manner, if the design requirement is not met, repairing the anti-wearing plate; S3, placing the floating ring on the anti-wear plate; checking whether a gap between a sealing ring and the anti-wear plate can meet the design requirement or not, if the design requirement is not met, replacing or trimming the sealing ring; S4, reloading the upper cover in order to adjust spring stress; and S5, reloading the floating ring and the water tank, and finishing the overhauling. The main shaft sealing overhauling method is accurate in data measurement, the sealing ring is protected from being worn eccentrically during running of a unit, the water leaking at the position is reduced, the service life of the sealing ring is prolonged, and the construction working period is shortened.